Water heater control system



July 2, 1946.-

Filed July 17, 1944 INVENTORQ CL RK ATTORNEY Patented July 2,1946

WATER HEATER oon'rnor. SYSTEM Clark M. Osterheld, Stoughton, Wis., assignor to McGraw Electric Company, Elgin, 11]., a corporation of Delaware Application July 17, 1944, Serial No. 545,353

My invention relates to electric heating and particularly to systems for controlling the energization of the electric heater for a domestic hot water tank.

Among the objects of my invention are the following: to provide a control system for the electric heater of a domestic hot water storage tank that shall cause immediate energization of the heater after closure of the time switch in case the tank contains a predetermined relatively large 6 Claims. (Cl. 219-39) amount of cold water, said energization continuing until all of the water in the tank is hot, and to cause energization of the heater with a predetermined time period of delay after closure of the time switch in case the tank contains a relatively small amount of cold water, said energization continuing until all of the water in the tank is hot.

Other objects of my invention will either be apparent from a description of one form of control system embodying my invention or will be pointed out in the course of such description and set forth particularly in the appended claims] In the drawing,

Figure 1 is a vertical, sectional view through a domestic hot water tank, with which is associated the control system embodying my invention,

which mass is held in proper operative position by an outer casing I9. An electric heater 2|, which may be the only heater, and, if so, is preferably located adjacent the bottom end portion of the tank, is provided and may be located in a tunnel member 23. I have illustrated anelectric heater 2| of the clamp-on type, and it is to be understood that any other heater usually used under such circumstances may be used instead of the heater 2|.

I provide a lower thermally-actuable heater control switch, designated by numeral 25 and comprising a tubular member 21 having a closed inner end and having its open outer end secured in water-tight engagement in an opening in tank ll adjacent to the lower end of the tank. An errpansion rod 29 is provided in the tube 21 and the free end of a substantially resilient contact arm 33. This contact arm is adapted to engage with and be disengaged from a substantially rigid contact arm 3'5, the two contact arms being supported by blocks 3! of electric-insulating material. The design, construction, and adjustment of the thermally-actuable switch 25 is such that when the tube 21 is surrounded by cold water, the-length of expansion rod 29 will be a minimum and the two contact arms 33 and 35 will be in electrical engagement with each other. When the tube 2'! is subject to hot water, the length of expansion rod 29 will be such that the resilient contact arm 23 will have been moved out of engagement with the rigid contact arm 35. While I have illustrated and described a specific embodiment of a thermally-actuable heater control switch, I do not desire to be limited thereto, since any other form of thermally-actuable switch effective for the same purpose may be used in place thereof.

When I speak of cold water, I mean water, the temperature of which is on the order of to F., and when I speak of hot water, I refer to water, the temperature of which is on the order of F., or slightly higher. The switch will be in closed position when the tube 21 is surrounded by cold water, and the position of the switchZli in its relation to the electric heater 2| is such that it will be moved to open position when substantially all of the water in the tank is hot.

I provide a thermal retarder heater control switch unit, designated generally by numeral 39,

which unit is positioned in heat-receiving relation on the tank at substantially the mid-height thereof. The thermal retarder heater control switch unit 39 is generally disclosed and claimed in my co-pending patent application, S. N. 537,-

V 941, filed May 29, 1944, and assigned to the same assignee as is the present application. While the thermal retarder switch unit disclosed and claimed in my above identified c0-pending application has only two switch units therein, the present thermal retarder switch unit has three such switches therein, the design of which is similar to those shown in the above identified application.

A first thermal heater control switch comprises a bimetal bar 4|, having one end thereof fixed. and having a pair of pivot plates 43 secured to the two spaced end portions of the free end thereof. I provide further a second bimetal bar 45, having two sharpened ends adapted to pivotally engage depressions in the pivot plates 43 and to be held in operative position therein by an over center spring 41, which is located in two aligned central longitudinally extending slots in the two bimetal bars 4| and 45, which will cause the free end of bar 45 to move with a snap action upon change of temperature. A contact bridging member 49 is insulatedly mounted on the free end of the second bimetal bar 45 and is adapted to engage with and be disengaged from a pair of fixed contact members 5! and 53. The design, construction, and adjustment of the first thermal switch, comprising the bimetal bars 4! and 45, is such that the contact bridging member 49 will be in engagement with the fixed contacts 5! and 53 when the temperature of the bimetal bars is on the order of 60 to 70 F., that is when the thermal retarder switch unit is subject to cold water in the tank. When the thermal retarder switch unit is subject to hot water in the tank, the contact bridging member 49 will be out of engagement with the contacts 5| and 53 and bimetal bar 45 will engage a stop 54.

I provide a second thermally-actuable switch, comprising a bimetal bar 55, having one end thereof fixedly secured and having a pair of pivot plates 51 secured to the two spaced end portions of the bar. A second bimetal bar 59, with a pair of shapened inner end portions fitting into the pivot plates 51, is held in proper operative position as by an over center spring 6i positioned in two aligned central longitudinally-extending slots in the two bars 55 and 59. which will cause movement of the free end of bimetal bar 59 with a snap action upon change of temperature. A contact bridging member 63, insulatedly mounted on the free end of the second bimetal bar 59, is adapted to engage with and be disengaged from a pair of fixed contact members 85 and B1. The first bimetal bar 55 of the second thermal switch is provided with a low-wattage heating coil 69 insulatedly mounted on and around the bimetal bar 55. The design, construction, and adjustment of the second thermal switch, comprising the bimetal bars 55 and 55, is such that the contact bridging member 93 will be out of engagement with contacts 85 and 81 at temperatures up to values on the order of 200 to 250 F. and will be in engagement with the contact members at temperatures above those values. When the second thermal switch is open, the bimetal bar 59 will be in engagement with a stop ill.

The thermal retarder switch unit includes a third switch, comprising a, first bimetal bar ii, having one end thereof fixed and having a pair of pivot plates 13 secured to the two spaced end portions thereof. A second bimetal bar 15, with sharpened inner end portions, is adapted to be held in pivotal engagement with the pivot plates 13 by an over center spring 11, which latter is positioned in two central 1ongitudina11y-extending slots in the adjacent ends of bimetal bars 'H and 15, so that movement of the free end of bimetal bar 15 will take place with a snap action upon change of temperature. A contact bridging member 19 is mounted on the outer end of the second bimetal .bar 15 and is adapted to engage with and be disengaged from two fixed contact members II and 83. I provide further a heating coil 95, which is insulatedly mounted on the first bimetal bar 1i and which, while the amount of energy translated into heat therein is relatively small, is so designed and constructed as to be traversed by the same current as traverses the heater 2i, as will be hereinafter set forth in detail. when the third thermal switch is open, the bimetal bar 15 will engage a stop 98. The design,

4 construction, and adjustment of the third thermal switch is such that it will be in open position at all temperatures below 250 to 259 but will be in closed position at all temperatures above that. The energy translated into heat in heating coil is such that bimetal bar i5 will have its temperature raised to 200 to 259 F. in from iiiteen to thirty minutes when traversed by the heater current.

I provide further a time-controlled switch. com prising two contact arms ill and which are adapted to be out of engagement with each other during on-pealt periods of a twenty-tour hour day but are adapted to be held in engaged position with each other during oif-pealr periods of a twenty-i our hour day by a continuously operative timer.

I provide two supply circuit conductors iii and 93, supply circuit conductor iii being connected to the first contact arm M of thc time-controlled switch. Contact arm 89 of the tlmecontrolled switch is connected by a conductor with fixed contact member 53. A conductor ll! connects the two fixed contacts 5| and Bi. A conductor 99 connects the conductor 91 to one terminal of the heater 85 of the third thermal switch and also connects conductor 91 to contact 55 of the second thermal switch. The contact 61 is connected by a conductor llli with the second contact arm 89 of the time-controlled switch. A conductor Illa connects contact'fi'i with one terminal of heating coil 69 on bimetal bar 55, the other terminal of this heating coil being connected by a conductor N15 to contact arm 35 of the lower thermally-actuablo switch 25. Contact arm 35 is connected by a conductor 10'! to one terminal of heater 2|, the other terminal of which is connected by a conductor I09 to the other terminal of heating coil 85 on bimetal bar H. Contact 83 of the third thermal switch is connected by a conductor ill to the first contact arm 81 of the time-controlled switch. Contact arm 33 of the lower thermally-- actuable switchis connected by a conductor M3 to the second supply circuit conductor fill.

Let it be assumed that a relatively large amount of hot water has been withdrawn from the tank during say daylight or oil-peak hours, the amount of water thus withdrawn being sufficient to ittl'l l the thermal retarder switch unit to he s to cold water. This will cause snap-acting ment of the contact bridging member t engagement with the fixed contacts ti and 5. The lower thermally-actuable switch it will, of course, also be in closed position. since it also will be subject to cold water. However, since the off-peak period has not yet been reached, no energlzatlon of the control circuit will be of fected. Let it now be assumed that the contact arm 81 is moved into engagement with contact arm 89, which will occur upon starting of an off-peak period, which, for illustrative purposes, may be considered to begin at say 10 p. m. or 11 p. m. This will cause an energizing circuit to be closed through the heater, traceable as follows: from supply clrcult'conductor 9| through engaged arms 81 and 89, through conductor 95, through the engaged contact bridging member 49 and contacts 53 and 5!, through conductors 91 and 95. through the heating coil B5 on the third thermal switch, through conductor I09, heater 2!, conductor I01, through the engaged contact arms 35 and 33, and through the conductor III to the second supply circuit conductor 93. The design, construction, and adjustment of the heating coil 85 on the bimetal bar H of the third through heater 2|, this circuit being traceable as follows: from supply circuit conductor 91 through conductor H I, engaged contact bridging member 19 and contacts 83 and BI, conductors 9'! and 59, through heating coil 85, through conductor Hi8, heater 2|, conductor lll'l, through the engaged contact arms 35 and 33, and through conductor H3 to the second supply circuit conductor 53.

This energization will continue, irrespective of thepcsition of the two contact arms 81 and 89 of the time-controlled switch, until substantially all of the water in the tank is hot, when deenergization of the heater 2! will be effected by the lower thermally-actuable switch 25. Thus, if for some reason an additional amount of hot water was withdrawn from the tank during the late night hours, so that the thermal retarder was again subject to cold water, the energization of the heater 2| would continue, irrespective of termination of the off-Beak period and opening of the time-controlled switch, until substantially all of the water in the tank was hot.

Let it now be assumed that only a relatively small amount of hot water was withdrawn from the tank during daylight hours, so that only the lower thermally-actuable switch 25 is subject to cold water, with attendant closure of switch 25. No energizing circuit would be closed until after closure of the time-controlled switch. The first thermal switch of the thermal retarder switch unit would be in open position, since the thermal retarder switch unit would be subject to hot water, and the second and third thermal switches of the thermal retarder switch unit would also be in open position.

As soon as contact arm 81 is moved into engagement with contact arm 89 by the time-controlled switch at the start of an oiT-peak period, an energizing circuit through heating coil 69 would be closed, traceable as follows: from supply circuit conductor 9|, through the time-controlled switch conta'ct arms 81 and 89, through conductors llll and H13, heating coil 69, conductor I05, through the contact arms 35 and 33, and

through conductor H3 to the second supply circuit conductor 93. The amount of energy translated into heat in the heating coil 69 is such that the temperature of the bar 55 will be raised to a value on the order of 200 to 250 F. in from four to six hours, and when this temperature has been reached, the contact bridging member 63 will be moved into engagement with contacts 61 and.

with a snap action to thereby close a heating circuit through the heater 2!, which circuit is substantially the same as that first above described upon closure of the time-controlled switch, this continuing until the third thermal switch has had its temperature raised with attendant snapacting closure of the switch controlled thereby. The energizing circuit through heater 2| will then be as follows: from the first supply circuit cuit for heater 2|, as will be noted, is entirely.

independent of the time-controlled switch. so that should additional hot water be withdrawn from the tank just before substantially all of the water in the tank is hot, energiz'ation of heater 2! will be continued, irrespective of opening or the time-controlled switch, until substantially all of the water in the tank is hot, when the lower thermally-actuable switch 25 will operate to deen'ergize the heater 2| and the whole system.

The system embodying my invention is therefore effective to selectively cause immediate energization of the heater upon closure of the timecontrolled switch, or to cause energization of the heater with a predetermined time delay, in accordance with the amount of cold water in the tank, such energization continuing until substantially all of the water in the tank is hot, irrespective of the possible opening of the time-controlled switch. This will ensure that' the tank is substantially full of not water at the start of the morning on-peak period.

Various modifications may be made in the system embodying my invention without departing from the spirit and scope thereof, and all. such modifications coming clearly within the scope of the appended claims shall be considered as covered thereby.

I claim as my invention:

1. A system for controlling the energization of an electric heater operatively associated with a domestic hot water tank subject to withdrawal v of hot water during a twenty-four hour day,

' a third thermal switch adapted to be in open pocomprising an electric heater, a lower thermallyactuable heater control switch mounted in heatreceiving relation on the tank adjacent to the lower end thereof and adapted to be in closed position when subject to cold water in the tank and to be in open position when subject to hot water in the tank, a time-controlled switch adapted to be in closed position during off-peak periods only, a three-switch thermal retarder heater control unit mounted in heat-receiving relation on the tank intermediate the ends thereof, comprising a first'thermal switch adapted to be in closed position when subject to cold water in the tank and in open position when subject to hot water in the tank, a second thermal switch adapted to be in open position when subject to cold and to hot water in the tank and to be in closed position when subject to a predetermined appreciably higher temperature, a heating coil for raising the temperature of said second switch to said predetermined temperature, the energization of said heating coil being controlled jointly by said lower and said time-controlled switches,

sition when subject to cold and to hot water in the tank and to be in closed position when heated to a predetermined appreciably higher temperature, and a beating coil for said third switch adapted to be transversed by the heater current and other electric connections between said electric heater and said switches to cause immediate energization of said heater upon closure of said time-controlled switch in case said first thermal switch of the thermal retarder unitis subject to cold water in the tank.

2. A system for controlling the energization of an electric heater operatively associated with a domestic hot water tank subject to withdrawal of hot water during a twenty-four hour day.

comprising an electric heater, a lower thermally-- actuable heater control switch mounted in heatreceiving relation on the tanlr adjacent to lower end thereof and adapted to be in, closed position when subject to cold water in the tank and to be in open position when subject to hot water in the tank, a time-controlled switch adapted to be in closed position during off-peak periods only, a three-switch thermal retarder heater control unit mounted in heat-receiving re-- lation on the tank intermediate the ends thereof, comprising a first thermal switch adapted to be in closed position when subject to cold water in the tank and in open position when subject to hot water in the tank, a second thermal switch adapted to be in open position when subject to cold and to hot water in the tank and to be in closed position when subject to a predetermined appreciably higher temperature, a heating coil for raising the temperature of said second switch to said predetermined temperature, the energization of said heating coil being controlled jointly by said lower and said time-controlled switches, a third thermal switch adapted to be in open position when subject to cold and to hot water in the tank and to be in closed position when heated to a predetermined appreciably higher temperature, and a heating coil for said third switch adapted to be traversed by the heater current and other electric connections between said electric heater and said switches to cause immediate energization of said heater upon closure of said time-controlled switch through said,

lower thermally-actuable switch and said first thermal switch.

3. A system for controlling the energizatlon of an electric heater operatively associated with a domestic hot water tank subject to withdrawal of hot water during a twenty iour hourday, comprising an electric heater, a lower thermally-actuable heater control switch mounted in heatreceiving relation on the tank adjacent to the lower end thereof and adapted to be in closed position when subject to cold water in the tank and to be in open position when subject to hot water in the tank, a time-controlled switch adapted to be in closed position during off-peak periods only, a three-switch thermal retarder heater control unit mounted in heat receiving re" lation on the tank intermediate the ends thereof, comprising a first thermal switch adapted to be in closed position when subject to cold water in the tank and in open position when subject to hot water in the tank, a second thermal switch adapted to be in open position when subject to cold and to hot water in the tank and to be in closed position when subject to a predetermined appreciably higher temperature. a heating coil for raising the temperature of said second switch to said predetermined temperature, the energizertion of said heating coil being controlled jointly by said lower and said time-controlled switches, a third thermal switch adapted to be in open position when subject to cold and to hot water in the tank and to be in closed position when heated to a predetermined appreciably higher temperature, a heating coil for said third switch adapted to be traversed by the heater current and other electric connections between said electric heater and said switches to cause immediate energiza-" tion of said heater upon closure oi said time-controlled switch through said lower thermally-actuable switch and said first thermal switch, said energization continuing through said lower thermally-actuable switch and said third thermal switch of the thermal retarder unit until substantially all of the water in the tank is hot.

4. A system for controlling the energization lit ' 8 an electric heater operatively associated with a domestic hot water tank subject to withdrawal of hot water during a twenty-four hour dot, comprising an electric heater, a lower thermally actuable heater control switch mounted in heatreceiving relation on the tank adjacent to the lower end thereof and adapted to be in closed position when subject to cold water in the tank and to be in open position when subject to hot water in the tank, a time-controlled switch adapted to be in closed postition during oil-peak periods only, a three-switch thermal retarder heater control unit mounted in heat-receiving re lation on the tank intermediate the ends thereof, comprising a first thermal switch adapted to be in closed position when subject to cold water in the tank and in open position when subject to hot water in the tank, a second thermal switch adapted to be in open position when subject to cold and to hot water in the tank and to be in closed position when subject to a predetermined appreciably higher temperature, a heating coil for raising the temperature of said second switch to said predetermined temperature, the energizetion of said heating coil being controlled jointly by said lower and said time-controlled switches, a third thermal switch adapted to be in open position when subject to cold and to not water in the tank and to be in closed position when heated to a predetermined appreciably higher temperature, and a heating coil for said third switch adapted to betraversed by the heater current and other electric connections between said electric heater and said switches to cause immediate energization of said heater upon closure of said time-controlled switch through said lower thermally-actuable switch and said first thermal switch, said energization continuing through said lower thermally-actuable switch and said third thermal switch of the thermal retarder unit until substantiaily all of the water in the tank is hot. deenergization of the heater being then effected by said lower thermally-actuable switch.

5. A system for controlling the energizatlon of an electric heater operatively associated with a, domestic hot water tank subject to withdrawal oi hot water during a twenty-four hour day, com prising an electric heater, a lower thermallyactuable heater control switch mounted in heatreceiving relation on the tank adjacent to the lower end thereof and adapted to be in closed position when subject to cold water in the tank and to be in open position when subject to hot water in the. tank, a time-controlled switch adapted to be in closed position during oil-peak periods only, a three-switch thermal retarder heater control unit mounted in heat-receiving relation on the tank intermediate the ends thereof, comprising a first thermal switch adapted to be in closed position when subject to cold water in the tank and in open position when subject to hot water in the tank, a second thermal switch adapted to be in open position when subject to cold and to hot water in the tank and to be in closed position when subject to a predetermined appreciably higher temperature, a heating coil for raising the temperature of said second switch to said predetermined temperature, the energizetion of said heating coil being controlled jointly by said lower and said time-controlled switches. a third thermal switch adapted to be in open position when subject to cold and to hot water in the tank. and to be in closed position when temperature, a heating coil for said third switch sesame 9 adapted to be traversed by the heater current and other electric connections between said electric heater and said switches to selectively cause energization of said heater immediately upon closure of said time-controlled switch in case said thermal retarder unit is subject to cold water in the tank and with a predetermined time delay period after closure of said time-controlled switch in case only the lower thermally-actuable switch is subject to cold water at the time of closure of said time-controlled switch.

6. A system for controlling the energizationoi an electric heater operatively associated with'a domestic hot water tank subject to withdrawal of hot-water during a twenty-four hour day, comprising an electric heater, a lower thermallyactuable heater control switch mounted in heatreeeiving relation on the tank adjacent to the lower end thereof and adapted to be in closed position when subject to cold water in the tank and to be in open position when subject to hot water in the tank, a tune-controlled switch adapted to be in closed position during off-peak periods only, a three-switch thermal retarder heater control unit mounted in heat-receiving relation on the tank intermediate the ends thereof, comprising a first thermal switch adapted to be in closed position when subject to cold water in the tank and in open position when subject to hot water in the tank, a second thermal sw 'aclr adapted to be in open position when subject to cold and to hot water in thetani: and to be in closed position when subject to a predetermined appreciably higher temperature, a heating coil for raising the temperature of said second switch to said predetermined temperature, the energization of said heating coil being controlled jointly by said lower and said time-controlled switches, a third thermal switch adapted to be in open position when subject to cold and to hot water in the tank and to be in closed position when heated to a predetermined appreciably higher temperature, a heatingcoil for said third switch adapted to be traversed by the heater current and other electric connec-' tions' between said electric heater and said 

